Epidermal Growth Factor Receptor (EGFR) is a member of the type 1 tyrosine kinase family of growth factor receptors, which play critical roles in cellular growth, differentiation, and survival. Activation of these receptors typically occurs via specific ligand binding, resulting in hetero- or homodimerization between receptor family members, with subsequent autophosphorylation of the tyrosine kinase domain. This activation triggers a cascade of intracellular signaling pathways involved in both cellular proliferation (the ras/raf/MAP kinase pathway) and survival (the PI3 kinase/Akt pathway). Members of this family, including EGFR and HER2, have been directly implicated in cellular transformation.
A number of human malignancies are associated with aberrant or overexpression of EGFR and/or overexpression of its specific ligands e.g. transforming growth factor α (Gullick, Br Med Bull 1991, 47:87-98; Modijtahedi and Dean, Int J Oncol 1994, 4:277-96; Salomon et al., Crit Rev Oncol Hematol 1995; 19:183-232). EGFR overexpression has been associated with an adverse prognosis in a number of human cancers, including NSCLC. In some instances, overexpression of tumor EGFR has been correlated with both chemoresistance and a poor prognosis (Lei et al., Anticancer Res 1999; 19:221-8; Veale et al., Br J Cancer 1993; 68:162-5). These observations suggest that agents that effectively inhibit EGFR receptor activation and subsequent downstream signaling may have clinical activity in a variety of human cancers, including NSCLC.
Tarceva™ (also known as erlotinib; OSI-774), a quinazoline, is an orally active, potent, selective inhibitor of EGFR tyrosine kinase. Erlotinib inhibits human EGFR tyrosine kinase with an IC50 of 2 nM (0.786 mg/mL) in an in vitro enzyme assay. This inhibition is selective for EGFR tyrosine kinase, results in cell cycle arrest at G1, and is reversible. Oral administration of erlotinib in mice has demonstrated a >70% reduction in EGFR autophosphorylation in human xenografts and marked growth inhibition of HN5 and A431 xenografts in nude mice has been demonstrated. In addition to single-agent activity in in vivo assay systems, erlotinib has been evaluated in combination with a number of chemotherapy agents to determine possible interactions. There was an additive interaction between erlotinib and paclitaxel, cisplatin, gemcitabine, and doxorubicin.
Lung cancer represents the leading cause of cancer-related mortality for both men and women in the United States. In 2000, it was estimated that 164,000 new cases would be diagnosed and 157,000 patients would die from this disease (Greenlee et al., CA Cancer J Clin 2001, 51:15-36). Approximately 75% of these patients would have had non-small cell histologies, with the majority presenting with inoperable Stage IIIB or Stage IV disease. For those patients with more limited disease at presentation (Stages I-IIIA), relapse following standard surgical therapy, with or without adjuvant or neoadjuvant chemo- and/or radiotherapy, is common. These findings result in an overall 5-year survival in non-small cell lung cancer (NSCLC) of ˜12% and serve to emphasize the unmet medical need in this disease.
The platinum compound cisplatin was the first chemotherapy agent to show clinical benefit in the management of locally advanced or metastatic NSCLC. Randomized clinical trials demonstrated improved response rates, quality of life, and survival compared with the best supportive care (Rapp et al. 1988). However, the magnitude of this improvement was modest—measured in weeks. Subsequently, a number of newer chemotherapy agents have been evaluated as single agents and in combination with the platinum salts in the first-line setting. The conclusion from these studies is that modern “doublet” chemotherapy appears to achieve response rates of 15%-20%, median time to disease progression of 3-4 months, and median survival of 7-8 months. The modest improvements in efficacy with combination therapies over the results obtained with cisplatin have established these therapies as a standard of care for patients with advanced NSCLC and an acceptable performance status (Non-Small Cell Lung Cancer Cooperative Group, Br Med 1 1995, 311:899-909; American Society of Clinical Oncology, J Clin Oncol 1997, 15:2996-3018; Breathnach et al., J Clin Oncol 2001; 19:1734-42).